Did you manually edit the permissions of the client's API key in your account preferences? That's the only way I would think this could happen. (The client keys aren't supposed to be editable, but they are currently.) In any case, if you unlink your account from the Sync account of the Zotero preferences (but keep your data) and then set up syncing again, it should work. Be sure to set it up with the same username (which is different from the account you're posting from here).